The present invention relates to a system for correction of the fuel injection time control upon variation in altitude, for a heat engine having an electronic fuel injection system, in particular a sequential and phased system.
As is known, electronic fuel injection systems for heat engines have an electronic central control unit which, in dependence on signals which it receives from various sensors (principally sensors detecting the speed of rotation and phase of the engine, and sensors detecting the pressure and temperature of the induction air) determines for example the density of the air in the manifold and the speed of rotation of the engine so that, in dependence on the volumetric capacity of the engine itself and the desired mixture strength, calculates from an interpolation on respective memorized mappings, the phase and the injection time of the fuel at the injectors, as well as the ignition advance.
The setting up and calibration of the injection system takes place at an external atmospheric pressure which is about 760 mm Hg, corresponding to a variable altitude generally up to 300 meters above sea level. During the various travels of the vehicle, at different altitudes, it can happen that as the external atmospheric pressure gradually falls (there is a reduction of about 80 mm Hg for each 1000 meters of height variation) there is an alteration of the operating characteristics of the engine, in particular of the volumetric capacity, in dependence on the different pressure losses in induction and exhaust. The phenomenon involves a variation in the mixture strength towards lean conditions which displace the slow running of the engine to lower values which are often not acceptable.